The invention relates to an air compressor of a compressed air system of a vehicle, including a piston pump with pistons, which are guided in working cylinders of a crankcase, and a crankshaft which is guided in the crankcase. At least one part of the crankcase is cast from aluminum. The crankcase includes at least one coolant duct for conducting coolant, which coolant duct is formed by at least one tube which is at least partially integrally cast into the crankcase.
Air compressors for utility vehicles conventionally have a cast steel crankcase which has no coolant ducts. In contrast, the cooling takes place in the cylinder cover, which is placed onto the crankcase, by means of air or liquid depending on the power required from the air compressor. The inlet and outlet valves, the mounting arrangement of the valves and at least one coolant duct and, if appropriate, a heat exchanger, are arranged in the cylinder cover.
With regard to installation in a vehicle, it is desirable for the air compressor to have the lowest possible weight. A generic air compressor is known from EP 0 470 021 A1, with the crankcase being cast from aluminum or from an aluminum alloy, and with the coolant ducts being formed as integrally cast aluminum tubes.
WO 2004/048765 describes a cylinder crankcase which has guide ducts for cooling, which guide ducts are formed by pre-shaped tubes which are concomitantly integrally cast during the casting of the crankcase.
The operating temperature prevailing in the crankcase is a significant factor with regard to the service life of the air compressor.
The invention is, in contrast, based on the object of further developing an air compressor of the above-mentioned type such that the air compressor has a longer service life. The longer service life is to be obtained by an improved cooling. Furthermore, it is intended to specify a method for producing an air compressor having these properties.
According to the invention, the crankcase is cast from aluminum. This results in a significant weight reduction in relation to cast steel crankcases. A weight saving of approximately 40% to 50% is obtained in relation to a crankcase produced from cast steel. The weight of the vehicle carrying the air compressor is, therefore, also advantageously reduced, which has a positive effect on fuel consumption.
Furthermore, the specific thermal conductivity of cast aluminum is approximately sixty times higher than that of cast steel, such that the heat generated during operation can be better dissipated, in particular to coolant which is conducted in at least one coolant duct of the crankcase.
The crankcase also includes at least one duct for conducting coolant. This measure reduces the operating temperature of the air compressor, such that the air compressor has a longer service life. The coolant duct is formed by at least one tube, which is at least partially integrally cast into the crankcase.
According to the invention, to supply coolant to the region of the crankcase between the working cylinders, the tube is bent into a plurality of windings in the shape of a figure “eight”. In this way, this region is also cooled, which has an advantageous effect on the service life of the compressor. Here, the bending of the tube into the shape of a Figure eight is a simple measure for supplying coolant to the region.
Advantageous refinements of the invention are described and claimed herein.
If the coolant duct were to open outward at a contact surface with respect to a cylinder cover in order to permit a continuation of the coolant duct through the coolant duct in the cylinder cover so as to provide a common coolant circuit of the crankcase and cylinder cover, this would lead to sealing problems at the contact surface. The coolant duct of the crankcase therefore preferably opens outward at a surface, which is not a contact surface with respect to a cylinder cover, of the crankcase, and may then be connected to the coolant duct of the cylinder cover by way of a separate connection.
For example, that surface, which is not the contact surface with respect to a cylinder cover, of the crankcase at which the coolant duct opens out is formed by an end surface, which is arranged substantially perpendicular to the crankshaft, with a supply pipe and a return pipe of the coolant duct being formed on the end surface.
According to one refinement, it is possible for at least one coolant duct of the crankcase to be integrated in a coolant circuit, which also includes a coolant duct which is assigned to the cylinder cover. The two coolant ducts may be connected in parallel or in series in the coolant circuit.
It is particularly preferable for the coolant duct to be formed by at least one tube which is produced from a non-aluminum material. Such a tube is preferably composed of steel and is cold or hot worked.
The crankcase is particularly preferably split into two crankcase parts at a parting plane which encompasses a central axis of the crankshaft. This firstly results in simple assembly and production of the crankcase.
Secondly, it is possible for a peripherally open oil duct to be formed in a contact surface of one of the crankcase parts, which oil duct connects a crankshaft bearing to at least one further crankshaft bearing for the supply of oil. Furthermore, it is then possible for the peripherally open oil duct to be peripherally closed off by the connection of the two crankcase parts and, on the one crankcase part, to open out at the end side into ports for a supply of oil. A core is therefore used to produce the oil duct during the casting process, which core can be removed in a simple manner after the casting process. The assembly of the one crankcase part on the other crankcase part serves not least to sealingly close off the oil duct at the periphery. The two crankcase parts are, for example, connected to one another by tension rods and centered with respect to one another by centering pins.
It is particularly preferable for all of the crankshaft bearings to be formed on the end side of the crankcase and to be divided by the parting plane.
Optimally, an upper crankcase part is provided with the at least one coolant duct and with the, in each case, upper part of a crankshaft bearing, and has at least one cylinder which guides a piston. In contrast, a lower crankcase part has the at least one oil duct and the, in each case, lower part of a crankshaft bearing.
The method for producing an air compressor having a crankcase into which at least one tube is integrally cast as a coolant duct includes at least the following steps:
a) shaping at least one tube according to at least one section of the coolant duct of the crankcase of the air compressor,
b) bending the tube into a plurality of windings in the shape of a Figure eight in order to supply coolant to the region of the crankcase between the working cylinders via the tube,
c) placing the at least one tube in a casting mold for at least one crankcase part of the crankcase; and
d) casting the at least one part of the crankcase from aluminum such that the at least one tube is at least partially integrally cast into the at least one crankcase part of the crankcase.
This approach has significant advantages in relation to coolant ducts which are integrally cast directly into the crankcase, that is to say by providing corresponding cores. This is because, in such a case, it is necessary when designing the profile of the coolant duct to make allowance for an arrangement of casting cores which is possible from a casting aspect, such that the coolant ducts cannot be designed with regard to the criterion of optimum cooling of the crankcase. In contrast, the method described above makes it possible for the tube to be shaped or bent so as to have an optimum coolant duct profile.